Causal quantum theory and the collapse locality loophole
Abstract
Causal quantum theory is an umbrella term for ordinary quantum theory modified by two hypotheses: state vector reduction is a welldefined process, and strict local causality applies. The first of these holds in some versions of Copenhagen quantum theory and need not necessarily imply practically testable deviations from ordinary quantum theory. The second implies that measurement events which are spacelike separated have no nonlocal correlations. To test this prediction, which sharply differs from standard quantum theory, requires a precise definition of state vector reduction. Formally speaking, any precise version of causal quantum theory defines a local hidden variable theory. However, causal quantum theory is most naturally seen as a variant of standard quantum theory. For that reason it seems a more serious rival to standard quantum theory than local hidden variable models relying on the locality or detector efficiency loopholes. Some plausible versions of causal quantum theory are not refuted by any Bell experiments to date, nor is it evident that they are inconsistent with other experiments. They evade refutation via a neglected loophole in Bell experimentsthe collapse locality loopholewhich exists because of the possible time lag between a particle entering a measurement device and a collapse taking place. Fairlymore »
 Authors:
 Centre for Quantum Computation, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 OWA (United Kingdom) and HewlettPackard Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ (United Kingdom)
 Publication Date:
 OSTI Identifier:
 20718298
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Physical Review. A; Journal Volume: 72; Journal Issue: 1; Other Information: DOI: 10.1103/PhysRevA.72.012107; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 74 ATOMIC AND MOLECULAR PHYSICS; BELL THEOREM; CAUSALITY; CORRELATIONS; EFFICIENCY; HIDDEN VARIABLES; LOCALITY; QUANTUM ENTANGLEMENT; QUANTUM MECHANICS; VECTORS
Citation Formats
Kent, Adrian. Causal quantum theory and the collapse locality loophole. United States: N. p., 2005.
Web. doi:10.1103/PhysRevA.72.012107.
Kent, Adrian. Causal quantum theory and the collapse locality loophole. United States. doi:10.1103/PhysRevA.72.012107.
Kent, Adrian. Fri .
"Causal quantum theory and the collapse locality loophole". United States.
doi:10.1103/PhysRevA.72.012107.
@article{osti_20718298,
title = {Causal quantum theory and the collapse locality loophole},
author = {Kent, Adrian},
abstractNote = {Causal quantum theory is an umbrella term for ordinary quantum theory modified by two hypotheses: state vector reduction is a welldefined process, and strict local causality applies. The first of these holds in some versions of Copenhagen quantum theory and need not necessarily imply practically testable deviations from ordinary quantum theory. The second implies that measurement events which are spacelike separated have no nonlocal correlations. To test this prediction, which sharply differs from standard quantum theory, requires a precise definition of state vector reduction. Formally speaking, any precise version of causal quantum theory defines a local hidden variable theory. However, causal quantum theory is most naturally seen as a variant of standard quantum theory. For that reason it seems a more serious rival to standard quantum theory than local hidden variable models relying on the locality or detector efficiency loopholes. Some plausible versions of causal quantum theory are not refuted by any Bell experiments to date, nor is it evident that they are inconsistent with other experiments. They evade refutation via a neglected loophole in Bell experimentsthe collapse locality loopholewhich exists because of the possible time lag between a particle entering a measurement device and a collapse taking place. Fairly definitive tests of causal versus standard quantum theory could be made by observing entangled particles separated by {approx_equal}0.1 light seconds.},
doi = {10.1103/PhysRevA.72.012107},
journal = {Physical Review. A},
number = 1,
volume = 72,
place = {United States},
year = {Fri Jul 15 00:00:00 EDT 2005},
month = {Fri Jul 15 00:00:00 EDT 2005}
}

Locality in quantum gravity and string theory
Breakdown of local physics in string theory at distances longer than the string scale is investigated. Such nonlocality would be expected to be visible in ultrahighenergy scattering. The results of various approaches to such scattering are collected and examined. No evidence is found for nonlocality from strings whose length grows linearly with the energy. However, local quantum field theory does apparently fail at scales determined by gravitational physics, particularly strong gravitational dynamics. This amplifies locality bound arguments that such failure of locality is a fundamental aspect of physics. This kind of nonlocality could be a central element of a possiblemore »